The explosion that killed at least 31 people Monday at Moscow’s busiest airport appears to be an act of terrorism, Russian President Dmitry Medvedev said on state TV.

Medvedev ordered additional security at Moscow’s other airports and transportation hubs, and Moscow police went on high alert in case of additional bombs.

The explosion occurred about 4:30 p.m. at the entrance of the international arrivals section of Domodedovo Airport, Itar-Tass said, citing a spokeswoman for the Russian Investigative Committee, Tatyana Morozova.

State TV aired video of the smoke-filled terminal, including what appeared to be bodies and luggage on the ground.

Russian state TV, citing Russian authorities, said the explosion was the act of a suicide bomber who stuffed a homemade bomb with small metal objects to make it more deadly, then activated it in a crowded area where many people were preparing for their flights. CNN could not independently verify those claims.